Finasteride 5mg is prescribed to treat benign prostatic hyperplasia (BPH), a condition where the prostate gland enlarges enough to interfere with urination. Sold under the brand name Proscar, this dose is specifically approved to improve urinary symptoms, reduce the risk of sudden urinary blockage, and lower the chances of needing prostate surgery. It’s a different dose from the 1mg version (Propecia), which is prescribed for hair loss.
How It Treats an Enlarged Prostate
Your body converts testosterone into a more potent hormone called DHT, which drives prostate growth. Finasteride blocks the enzyme responsible for that conversion, cutting DHT levels in the blood by roughly 65 to 70% and lowering DHT inside the prostate tissue by about 66%. With less DHT fueling growth, the prostate gradually shrinks. In clinical trials lasting five years, prostate volume dropped by about 25% on average, with the maximum reduction occurring around the two-year mark and holding steady through year five.
That shrinkage translates to real relief. As the prostate gets smaller, it puts less pressure on the urethra, so the stream of urine gets stronger and the constant urge to go, especially at night, eases up. Finasteride also reduces the risk of acute urinary retention, a painful emergency where the bladder can’t empty at all, and makes it less likely you’ll need surgical procedures to remove prostate tissue.
What to Expect and How Long It Takes
Finasteride is not a fast-acting drug. Because it works by gradually shrinking the prostate rather than relaxing muscles around it, noticeable symptom improvement can take several months. The prostate continues to shrink over roughly two years before leveling off, so the full benefit builds slowly. Many doctors prescribe it alongside an alpha-blocker (a drug that relaxes the muscles around the prostate for quicker relief) to cover both the short and long term. This combination has been shown to reduce the risk of BPH getting progressively worse over time.
Finasteride is taken once daily and is meant to be used continuously. Stopping it allows DHT levels to rise again, and the prostate will gradually return to its previous size.
Why 5mg Instead of 1mg
The 1mg dose was developed specifically for male pattern hair loss, where a smaller amount of DHT suppression is enough to slow or stop thinning at the scalp. The prostate is a larger organ with more DHT activity, so it requires the higher 5mg dose to achieve meaningful shrinkage. Some people split 5mg tablets with a pill cutter and take a quarter daily as a cheaper alternative to the 1mg hair loss prescription, though this is an off-label use and the tablets aren’t scored for even splitting.
Sexual Side Effects
The most discussed side effects of finasteride 5mg are sexual. In clinical studies, erectile difficulties affected roughly 10% of men taking finasteride for BPH compared to lower rates on placebo. Reduced sex drive occurred in about 8%, and changes in ejaculation in about 6%. These numbers come from trials where men didn’t know whether they were taking the drug or a placebo.
Interestingly, when researchers studied what happens if men are told they might experience sexual side effects, the rates jumped dramatically: erectile difficulties reported by 31%, decreased libido by 24%, and ejaculation changes by 16%. This gap suggests that expectation plays a significant role, a phenomenon known as the nocebo effect. A large review of over 17,000 patients found that sexual side effects were statistically more common at the 5mg BPH dose than in men taking 1mg for hair loss, where the increase over placebo was not statistically significant.
For most men, these side effects resolve after stopping the medication. A small number of men report persistent sexual symptoms after discontinuation, a topic of ongoing medical debate.
Effect on PSA Screening
Finasteride cuts PSA (prostate-specific antigen) levels by about 50%. PSA is the blood marker used to screen for prostate cancer, so this matters. If you’re taking finasteride and get a PSA test, your doctor needs to double the result to get an accurate reading. Without that adjustment, a rising PSA that should trigger further evaluation could look normal and get missed. Make sure any provider ordering a PSA test knows you’re on finasteride.
Finasteride and Prostate Cancer Risk
A landmark trial of nearly 19,000 men found that those taking finasteride 5mg daily developed about 30% fewer prostate cancers overall than men on placebo: 10.5% versus 14.9%. That reduction came entirely from fewer low-grade, slow-growing cancers. Early results raised concern about a small uptick in high-grade cancers (3.5% in the finasteride group versus 3% in the placebo group), but later analysis determined this was likely a detection artifact. Finasteride shrinks the prostate, which makes biopsies more accurate at finding aggressive cancers that were already there. After adjusting for this detection bias, researchers at the National Cancer Institute concluded that high-grade tumors were no more likely in men taking finasteride. Despite these findings, finasteride is not FDA-approved for prostate cancer prevention.
Handling Precautions
Women who are or could become pregnant should not handle broken or crushed finasteride tablets. The drug can be absorbed through the skin and may cause abnormalities in a male fetus. Intact tablets have a coating that prevents skin contact with the active ingredient during normal handling, so the risk applies only to tablets that are damaged, split, or crushed. If you’re splitting tablets at home for any reason, keep them away from anyone who could be pregnant.
Cost and Insurance Coverage
Generic finasteride 5mg is inexpensive. A 90-day supply has a retail sticker price around $165, but pharmacy discount programs regularly bring that down to under $10 for the same quantity. Most Medicare and insurance plans cover the 5mg dose when prescribed for BPH. Coverage for off-label uses like hair loss is less common, which is one reason some people buy the 5mg tablets and split them.